Normally when plate and sheet drilling and cutting machines are used to drill and or cut plate, the plate or product being drilled or cut has to be held or clamped by clamping assembly on any support surface such as a table, at least minimally during the drilling or cutting. In this case the drill or cutter is independently driven by a motor which is raised and lowered by a servo motor. And the clamping assembly is driven down by pneumatic or hydraulic means and guided by linear bearings.
Most clamping assemblies have a measuring means which comprises a linear measuring device which is used to determine the position of the top of the plate to be drilled with respect to the bottom of the drill so that the drill only goes down a set distance. This linear measuring device is often a linear Variable Displacement transducer (LVDT) or via a rack and pinion driving an encoder. This measuring device works by measuring the length of the extension of the clamp cylinders, and therefore the top of the plate to be machined.
There are problems with this type of arrangement whereby the drilling and clamping actions are independent which cause problems in sequencing whereby delays occur while waiting for the clamping before drilling can commence.
The clamp assembly includes an air or hydraulic cylinder which is attached to a clamp foot means which in turn leads to a clamp plate which abuts/pushes with a clamp force on the product to be drilled or cut eg a plate or sheet. The clamp foot must be driven down with the clamp cylinders to precede the drill so that the plate is clamped prior to drilling or machining commencing. The clamping force is set by setting the air or hydraulic cylinder pressure.
The linear measuring is time consuming and can be inaccurate. Problems can also arise when the clamping causes deflection of the plate which can effect the linear measure distance which is not able to pick up such small changes which still can greatly effect drilling where by the plate may not be drilled or cut.
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